1. Field of the Invention
The present invention relates to method and apparatus for testing of driving circuit for judging approval or disapproval of a driving circuit used in display control of, for example, liquid crystal display device.
2. Description of the Related Art
To realize a color display in a liquid crystal display device, by controlling the voltage applied to each pixel of the liquid crystal display device, an arbitrary luminance is obtained, while an arbitrary chrominance is obtained by combination of red light, blue light and green light.
The value of the voltage applied to each pixel is the voltage corresponding to the picture signal to be displayed being converted into the voltage used in each pixel display by the driving circuit.
By varying the input value of the voltage entering the driving circuit, the output value of the voltage produced from the driving circuit also changes. Thus, by controlling the voltage applied to the pixel, the luminance and chromainance of display are controlled.
To control the luminance and chrominance, a linear relation is required between the change of the input value of the voltage applied to the driving circuit and the change of the output value of the voltage produced from the driving circuit. In other words, uniform and arbitrary display is not achieved unless the driving circuits connected to the pixels for displaying in the liquid crystal display device possess equal input and output relations.
As shown in FIG. 3, a driving circuit 3 of a liquid crystal display device comprises a sampling hold circuit 8, a transfer circuit 9, an operational amplifier circuit 10, and an output circuit 11. These circuits 8, 9, 10, 11 comprise transistors, resistors, capacitors, switching circuits and other. Accordingly, if the transistor characteristic or the resistor or capacitor value is improper, a current may flow although the switching circuit is cut off, or a leakage current may flow in the wiring. In such a case, the driving circuits 3 connected to the pixels for displaying in the liquid crystal display device do not possess equal input and output relations, and uniform and arbitrary display is not achieved, and the display quality is lowered. It is therefore required to judge if the driving circuits 3 connected to the pixels possess equal input and output relations or not.
Hitherto, by feeding arbitrary two values c, d in the driving circuit as input value .alpha.1, and setting the allowable range for the output value .beta.1 to the input of values c, d, it is approved when the output value .beta.1 is in the allowable range for both c and d.
FIG. 1 is a graph for explaining the prior art, which shows the relation between the input value .alpha.1 and output value .beta.1. Supposing the input value .alpha.1 to be c, the coordinate is Cc if the output value .beta.1 is C1, the coordinate is Cb is C2, and the coordinate is Ca if C3. Hence, the allowable range of the output value .beta.1 for the input value c is from C1 to C3.
C1, C2 and C3 of output value .beta.1 are in a relation as represented by Formula 1, and the coordinates Ca, Cb, Cc commonly possess the approved output value .beta.1. EQU C1&lt;C2&lt;C3 Formula 1
Similarly, when the input value .alpha.1 is d, the coordinate is Da if the output value .beta.1 is D1, the coordinate is Db if D2, and the coordinate is Dc if D3. Hence, the allowable range of the output value .beta.1 for the input value d is from D1 to D3.
D1, D2 and D3 of output value .beta.1 are in a relation as represented by Formula 2, and the coordinates Da, Db, Dc commonly possess the approved output value .beta.1. EQU D3&lt;D2&lt;D1 Formula 2
Therefore, all driving circuits having the combination of the coordinates Ca, Cb, Cc and the coordinates Da, Db, Dc are approved.
Suppose there is a relation of Formula 3 between output values C3 and C1, D1 and D3, where E is a constant. EQU C3-C1=D1-D3=E Formula 3
The line R1 linking the coordinate Ca and coordinate Da and the line R2 linking the coordinate Dc and coordinate Dc are parallel to each other, and the output value .beta.1 with respect to the input value .alpha.1 always has a difference of constant E.
Between the line R3 linking the coordinate Ca and coordinate Dc and the line R4 linking the coordinate Dc and coordinate Da, the line R3 has the larger change of the output value .beta.1 accompanying the change of the input value .alpha.1, and the relation between the input value and output value is different.
Supposing the desired relation between the input value .alpha.1 and output value .beta.1 to be the line R5 linking the coordinate Cb and coordinate Db, in the prior art, the driving circuit possessing the relation of the lines R1, R2, R3, R4 not possessing the relation of the line R5 is also approved.
Therefore, the driving circuits possessing different input and output relations are judged to possess the same input and output circuits, and the display is not controlled uniformly, and hence the display quality is lowered.
The invention hence presents a method for testing of driving circuit for judging approval or disapproval of driving circuit by making use of the relation between a first signal fed in the driving circuit and a second signal produced from the driving circuit corresponding to the first signal, comprising:
a step of feeding a predetermined first signal in the driving circuit,
a step of storing a second signal produced from the driving circuit corresponding to the first signal,
a step of calculating the numerical value corresponding to the relation in plural sets of the first signal and second signal, and
a step of judging approval or disapproval of the driving circuit by comparing the criterion corresponding to the relation between the predetermined first signal and second signal with the numerical value obtained by operation in the calculating step.
The invention also presents a method for testing of a driving circuit, in which the driving circuit receives mutually different plural first signals.
The invention also presents a method for testing of a driving circuit, in which the change rate of the second signal and the second signal corresponding to the predetermined first signal are calculated from the plural first signals and the plural second signals obtained corresponding to the plural first signals.
The invention also presents a method for testing of a driving circuit, in which the change rate of the second signal obtained by calculation above and the second signal corresponding to the predetermined first signal are compared respectively with the standard change rate predetermined in relation to the second signal and the standard second signal corresponding to the predetermine first signal, and the driving circuit being tested is judged to be approved when coinciding in both cases.
Furthermore, the invention presents an apparatus for testing of a driving circuit for judging approval or disapproval of driving circuit by making use of the relation between a first signal fed in the driving circuit and a second signal produced from the driving circuit corresponding to the first signal, comprising:
input means for feeding a predetermined first signal in the driving circuit,
memory means for storing a second signal produced from the driving circuit corresponding to the first signal,
arithmetic means for calculating the numerical value corresponding to the relation of plural sets of first signal and second signal, and
judging means for judging approval or disapproval of driving circuit by comparing the criterion corresponding to the relation between the predetermined first signal and second signal with the numerical value obtained by the arithmetic means.